Timing product delivery feed rate

I have a product that i need to time the feed rate of product delivery to a machine (for display purposes only at this stage).


i want to trigger the timer by a photocell that is sensing the product.



timing to occur from the front edge of product to the front edge of the next product there is small gap between the products, this gives a pulse on - off - On with an approx mark space ratio of 3 to 1 (3 times on longer than off)


the PE cell is a point I/O input to a 1756-L72 CPU with Version V28.


has anyone done this successfully?

• i tried to use the PE to latch a bit

• then used the latched bit in series with the PE again to drive the unlatch statement
• used a TON timer to time the duration of the latched bit

When you say feed rate, that implies parts over time. Are you looking for parts per minute, or parts per hour, or parts per second?

The rate will be a factor on how you do this. But let's say it's parts per minute.
Have the Pulse increment a Counter one value for each pulse.

Create a periodic task that runs every 1000 ms.
Inside the task..
Multiply Counter value x 60= parts per minute, store in register to display.
Reset the counter.

For Slower rates increase periodic task to 2000 or 5000 and multiply by 30 or 12.

For High Speed rates, you will need a different setup.

You can measure the time between each pulse. It takes 3 rungs of logic.

Rung 1. Use your PE to one shot an OTE.
Rung 2. XIC of OTE Move Timer.ACC into a Storage DINT. Then Divide 60000 by Storage DINT and place in a Display DINT.
Rung 3. XIO of OTE Run Timer.

This will give you a Real Time PPM in your Display DINT.

Many thanks for your replies.

• Ken, i need to know the time between pulses to fine tune a packaging machine that has arrived, it has a function where if it acts too fast it can take 2 products instead of 1, the operation is it takes one and leaves one for the next machine to take. if it acts on both triggers a jam up occurs. your reply has helped me with some reporting of same machine i also need to do.

• Cwal61, many thanks i was close but had some timing issues so your solution is best, thanks again.